An on-board distillation system to reduce cold-start hydrocarbon emissions from gasoline internal combustion engines

In modern port fuel injected engines, 60--95% of all hydrocarbon (HC) emissions occur during the cold-start and warm-up periods, generally within the first 2 minutes of engine operation after a prolonged soak. The relatively low volatility of gasoline at moderate to cold temperatures leads to elevated levels of engine-out hydrocarbon emissions: It has been reported that only 10--20% of gasoline injected during a 20°C cold-start evaporates to join the combustible air/fuel mixture. To compensate for poor fuel vaporization, 8--15 times the stoichiometric amount of fuel will be injected to ensure there is ample fuel vapor for robust starting. The end result is an overabundance of fuel vapor for most starting conditions in addition to a copious amount of liquid fuel that never enters the combustible mixture. The result is high engine-out emissions, which---left unchecked by the catalysts---become high tailpipe emissions; conventional three-way catalysts may not reach "light-off" (50% conversion efficiency) temperature for 30--40 seconds or more during a normal drive. The combination of high engine-out HCs with catalytic converter inactivity during starting and warm-up is the primary cause of high cold-start tailpipe HC emissions.; The On-Board Distillation System (OBDS) was developed to extract, from gasoline, a highly volatile fuel for use during the cranking and warm-up periods in lieu of gasoline. The system was installed on a 2001 Lincoln Navigator to explore the emissions reductions possible on a large vehicle with a large-displacement engine. The fuel and spark calibration of the electronic engine controller were modified to exploit the benefits of the OBDS startup fuel.; The key benefits provided by the OBDS fuel relative to standard gasoline were (1) intimate knowledge of startup fuel volatility, allowing aggressive fuel and spark calibration; (2) improved mixture preparation allowing >75% reduction of cranking fuel, elimination of air-fuel mixture enrichment during the warm-up period, and significant extension of warm-up ignition timing retard; (3) 55% decrease in catalyst light-off time; and (4) emissions reductions over the FTP drive cycle of 81% for regulated hydrocarbons (NMOG).